Bladder cancer is the most common cancer among genitourinary cancers, and its causes are relatively well known. It is known that the cancer develops from stimulation of the bladder wall when cigarette smoke or several chemicals (for example, leather dying paint, air pollutants, artificial sweeteners, and nitrates) are absorbed into the body and excreted in the urine.
A conventional bladder cancer test uses a method of finding abnormal cells in the urine but it has a low accuracy. Moreover, a cystoscopy test in which a catheter is inserted into the bladder and extracts suspected tissues is an invasive method and has relatively high accuracy.
In general, although a patient survival rate increases when bladder cancer is diagnosed at an early stage, it is difficult to diagnose bladder cancer at an early stage. A currently used bladder cancer diagnosis method uses a method in which a part of the body is incised, but it is difficult to diagnose bladder cancer at an early stage. Bladder cancer is classified as superficial or invasive cancer based on invasion of the bladder muscle layer, and about 30% of patients on average have the invasive bladder cancer at the time of the diagnosis. Accordingly, in order to increase a patient survival period, early diagnosis upon formation of a small range of lesions is best. Therefore, there is an urgent need to develop a diagnosis method that is more efficient than various existing bladder cancer diagnosis methods, that is, a method that can diagnose at an early stage and handle a large amount of samples, and a bladder cancer specific biomarker having a high sensitivity and specificity.
Meanwhile, APE1/Ref-1(apurinic/apyrimidinic endonuclease1/redox factor-1) is a multifunctional protein consisting of 318 amino acids including an oxidation-reduction region (redox region) and a DNA repair region. The protein is known to have a function of the APE1 recovering the damaged region when the DNA is damaged, and a redox function of the transcription factors, for example, AP-1 and NF-kB (Gurusamy, Malik et al. 2007). The transcription factor redox function of the APE1/Ref-1 facilitates transcription by reducing residue of the oxidized states of cysteine in the DNA bonding site of a plurality of transcription factors (Xanthoudakis, Miao et al. 1994; Tell, Damante et al. 2005).
The APE1/Ref-1 is present in all cells and tissues, and it is known that intracellular expression locations vary depending on the cells. The expression of the APE1/Ref-1 is regulated at the transcription and post-transcription levels. Reactive oxygen species (ROS) is a major cause of increased expression of the APE1/Ref-1. When macrophages and lymphocytes are treated with hydrogen peroxide and hypochlorous acid (HOCl), the expression of intracellular APE1/Ref-1 increases and this increase in the expression of the APE1/Ref-1 is considered as an adaptive response of the cells for protection against cell toxicity and oxidative stress (Ramana, Boldogh et al. 1998).
Various intracellular locations of the APE1/Ref-1 have been reported. Those diverse intracellular locations may be understood by analyzing protein sequences of the APE1/Ref-1. A nuclear localization signal (NLS) is present at an amino acid terminal side of the APE1/Ref-1 (Jackson, Theriot et al. 2005). APE1/Ref-1 can translocate from nucleus to cytoplasm in response to a nuclear export signal (NES) dependent on the S-nitrosation of cysteines 93 and 310 (Qu, Liu et al. 2007). Expression of the APE1/Ref-1 protein is also observed in mitochondria (Chattopadhyay, Wiederhold et al. 2006).
The APE1/Ref-1 protein created within cells may be isolated outside the cells. Inflammatory response and cell activation by endotoxin in the macrophage allow the APE1/Ref-1 to be isolated from the cells. Therefore, accurate measurement of the APE1/Ref-1 is important to understand potential functions of the APE1/Ref-1 in many biological processes, for example, heart cerebrovascular disease, inflammatory disease, and tumors.
However, it has not yet been reported that the APE1/Ref-1 protein acts as a bladder cancer diagnosis marker, and the resulting studies have not been made. Accordingly, there is an urgent need to develop a biomarker which can increase the patient survival rate by early diagnosis of bladder cancer from the blood at the time of health examinations with ease.